Instance Methodswift 6.1.2_Concurrency

compactMap(_:)

Creates an asynchronous sequence that maps an error-throwing closure over the base sequence’s elements, omitting results that don’t return a value.

iOS: 13.0+
macOS: 10.15+
tvOS: 13.0+
watchOS: 6.0+

@preconcurrency func compactMap<ElementOfResult>(_ transform: @escaping (Self.Element) async throws -> ElementOfResult?) -> AsyncThrowingCompactMapSequence<Self, ElementOfResult>

Mangled symbol

sSci12_ConcurrencyE10compactMapyAA020AsyncThrowingCompactC8SequenceVyxqd__Gqd__Sg7ElementQzYaKclF What are these?

FNV24 hash: 1F8ZN

Parameters

transform: An error-throwing mapping closure. transform accepts an element of this sequence as its parameter and returns a transformed value of the same or of a different type. If transform throws an error, the sequence ends.

Returns

An asynchronous sequence that contains, in order, the non-nil elements produced by the transform closure. The sequence ends either when the base sequence ends or when transform throws an error.

Use the compactMap(_:) method to transform every element received from a base asynchronous sequence, while also discarding any nil results from the closure. Typically, you use this to transform from one type of element to another.

In this example, an asynchronous sequence called Counter produces Int values from 1 to 5. The closure provided to the compactMap(_:) method takes each Int and looks up a corresponding String from a romanNumeralDict dictionary. Since there is no key for 4, the closure returns nil in this case, which compactMap(_:) omits from the transformed asynchronous sequence. When the value is 5, the closure throws MyError, terminating the sequence.

let romanNumeralDict: [Int: String] =
    [1: "I", 2: "II", 3: "III", 5: "V"]

do {
    let stream = Counter(howHigh: 5)
        .compactMap { (value) throws -> String? in
            if value == 5 {
                throw MyError()
            }
            return romanNumeralDict[value]
        }
    for try await numeral in stream {
        print(numeral, terminator: " ")
    }
} catch {
    print("Error: \(error)")
}
// Prints "I II III Error: MyError() "